Showing papers by "Radhakrishna G. Pillai published in 2023"
TL;DR: In this article , the performance of a novel pre-blended grout produced on an industrial scale using the fluidity and fluidity retention tests, standard, wickinduced, pressure-induced, and inclined tube bleed tests was studied.
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TL;DR: In this article , a proof-of-concept study was conducted to validate that a thin layer of grout around the strand will be sufficient for a galvanic anode (connected to the end of the strand at outside the tendon anchorage) to protect the strand portions inside the duct/anchorage.
Abstract: Grouted post-tensioned (PTd) concrete systems are widely used in long-span segmental bridges with a target service life of 100+ years. However, the usage of inadequate grout materials and grouting practices have resulted in the formation of unwanted air voids in the duct, which in turn led to premature corrosion (say, within about 20 years) of strands and failure of tendons. Also, the re-grouting/repairing of void regions have led to localized corrosion of strands at the interface between the dissimilar base-grout (usually carbonated) and repair-grout. This study aims (i) to quantify the galvanic corrosion at the void region in a PTd system re-grouted with a dissimilar grout and (ii) to develop cathodic protection system to protect PTd anchorage regions. Specimens simulating the re-grouted strand-grout-air (SGA) interface were prepared with prestressing steel wires and cementitious grout. The macro-cell current (galvanic current) between the prestressing steels embedded in carbonated base-grout and repair-grout indicated that galvanic corrosion can be possible at the SGA interface – reducing the long-term structural reliability of re-grouted PTd bridges. In addition, the feasibility of galvanic anode cathodic protection system to protect PTd anchorage regions was assessed. For this, a proof-of-concept study was conducted to validate that a thin layer of grout around the strand will be sufficient for a galvanic anode (connected to the end of the strand at outside the tendon anchorage) to protect the strand portions inside the duct/anchorage.
TL;DR: In this article , a short-term test method (Galvanic Anode Performance (GAP) test) was developed to assess the longevity of Galvanic anodes (GAs) in reinforced concrete (RC) structures.
Abstract: NACE impact report (2016) states that nearly 50% of reinforced concrete (RC) structures experience major repair in about ten years. The existing approach of patch repair does not address the root cause and may not be durable – resulting in re-repair and huge economic loss. Galvanic anodes (GAs) are gaining widespread acceptance to achieve maintenance-free repair life for a few decades. However, a few GAs with inadequate characteristics are prematurely failing (within a few months). There are no short-term test methods to evaluate the longevity of GAs. Therefore, this work focuses on developing a short-term test method (Galvanic Anode Performance (GAP) test) to assess the longevity of GAs. For this, the GAP specimen was designed by simulating CP-protected RC structure as follows: (i) GA embedded in bedding mortar (i.e., anode), (ii) Nichrome mesh (i.e., cathode simulating rebars in RC structures), (iii) position of anode and cathode, (iv) application of potential difference (0.5, 1, 5, 10, 20, and 30 V) to accelerate the degradation of GAs, and (v) electrolyte to simulate conductivity of concrete. Applied potentials > 5 V could not capture the difference in characteristics of GAs. However, potential differences of 0.5, 1, and 5 V could show the true behavior of GAs in various exposure conditions. Then, an approach is proposed to evaluate the service life of GAs. Possible reasons for the premature failure of anodes were investigated by evaluating pH and pore volume of encapsulating mortar. The GAP test can help practicing engineers to estimate the longevity of GAs.
TL;DR: In this paper , the authors provide an overview of the state-of-the-art of durability design in reinforced concrete and highlight the strengths and weaknesses of the current practices and recommend a multi-barrier strategy to achieve long-term performance and corrosion resistance.
Abstract: Reinforced concrete is, in general, a very durable system. However, as designers pursue more efficient structural designs and subject these structures to more aggressive environments, these systems become increasingly susceptible to corrosion. Corrosion of steel reinforcement is one of the more prevalent mechanisms of deterioration in reinforced concrete systems. As the world’s infrastructure ages, the cost of repair and replacement of these systems increase at rapid rates. As new models, designs, materials and construction methods become available, the service life of these systems should be extended. This Special Issue initially focuses on current practices used throughout the world to mitigate corrosion of the steel reinforcement embedded in concrete. Alexander et al., Li and Ueda, and Geiker et al. provide an overview for durability based design in South Africa, Asia and Europe. The authors note that both prescriptiveand performance-based methods are currently in use with the objective of ensuring durability. All authors note the use of models, especially models to predict the ingress of chlorides into concrete, should be used to better predict the service life. However, Alexander et al. critique exposure classifications and conclude that both rational service life designs and relevant environmental exposure classifications are sorely needed. The authors also recommend that exposure classifications account for the various factors that influence reinforcement corrosion and the resulting structural damage. Li and Ueda review the state-of-theart of durability design in Asia and highlight the strengths and weaknesses of the current practices. The authors ultimately recommend a ‘multi-barrier’ strategy to achieve long-term performance and corrosion resistance of reinforced concrete systems. Geiker at al. provide a European perspective on durability design and argue that designers must understand basic deterioration mechanisms and resulting damage to better design the infrastructure systems. The authors also note that service life models should include the time from corrosion initiation to the end of life (i.e., the propagation phase) to provide more resilient designs. In addition to the design for durability perspectives from the different regions, understanding how to better predict and quantify factors that influence the service life are critical for improving resilience. Ogunsanya et al. present how the use of different de-icing chemicals can influence the critical chloride threshold, a critical parameter for assessing service life. Boschmann Käthler et al. present a review of how the critical chloride threshold values are assessed and make recommendations on how to quantify these critical chloride values. Interestingly, such a critical parameter for assessing the service life of reinforced concrete system has no standardized testing protocol (although advances are underway in several locales). Ahmed and Vaddey present interesting work on chloride testing of various cementitious systems and recommend that water-soluble chloride testing be used to quantify chlorides in concrete. Standardizing testing requirements are essential for ensuring corrosionresistant structures and yet the pursuit is on-going. Shakouri and Dhandapani & Santhanam focus on buildup and transport rates of chlorides in concrete systems. Shakouri reported on the surface build-up rate of chlorides and assesshow these build-up rates influence service life. He concluded that a universal test is needed to assess surface chlorides; interestingly, this is another critical input parameter for assessing the service life and yet there is limited standardization. Shakouri also reported the need for long-term field data. Dhandapani and Santhanam compared various test methods currently used to quantify chloride transport rates under various exposure conditions and report good correlation between several testing methods. Although much of the literature on chloride transport and service life of reinforced concrete systems focus on uncracked concrete, cracking in concrete is common. Yet limited work has been performed to assess how cracks influence corrosion and resulting service life of reinforced concrete systems. O’Reilly et al. assessed the corrosion performance of reinforced concrete specimens containing narrow cracks and reported that these narrow cracks can promote corrosion and potentially